Documentation/fb/vesafb.txt

   1
   2 What is vesafb?
   3 ===============
   4
   5 This is a generic driver for a graphic framebuffer on intel boxes.
   6
   7 The idea is simple:  Turn on graphics mode at boot time with the help
   8 of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k
   9 (and other) ports do.
  10
  11 This means we decide at boot time whenever we want to run in text or
  12 graphics mode.  Switching mode later on (in protected mode) is
  13 impossible; BIOS calls work in real mode only.  VESA BIOS Extensions
  14 Version 2.0 are required, because we need a linear frame buffer.
  15
  16 Advantages:
  17
  18  * It provides a nice large console (128 cols + 48 lines with 1024x768)
  19    without using tiny, unreadable fonts.
  20  * You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11
  21    support for every VBE 2.0 compliant graphics board).
  22  * Most important: boot logo :-)
  23
  24 Disadvantages:
  25
  26  * graphic mode is slower than text mode...
  27
  28
  29 How to use it?
  30 ==============
  31
  32 Switching modes is done using the vga=... boot parameter.  Read
  33 Documentation/svga.txt for details.
  34
  35 You should compile in both vgacon (for text mode) and vesafb (for
  36 graphics mode). Which of them takes over the console depends on
  37 whenever the specified mode is text or graphics.
  38
  39 The graphic modes are NOT in the list which you get if you boot with
  40 vga=ask and hit return. The mode you wish to use is derived from the
  41 VESA mode number. Here are those VESA mode numbers:
  42
  43     | 640x480  800x600  1024x768 1280x1024
  44 ----+-------------------------------------
  45 256 |  0x101    0x103    0x105    0x107
  46 32k |  0x110    0x113    0x116    0x119
  47 64k |  0x111    0x114    0x117    0x11A
  48 16M |  0x112    0x115    0x118    0x11B
  49
  50 The video mode number of the Linux kernel is the VESA mode number plus
  51 0x200.
  52
  53  Linux_kernel_mode_number = VESA_mode_number + 0x200
  54
  55 So the table for the Kernel mode numbers are:
  56
  57     | 640x480  800x600  1024x768 1280x1024
  58 ----+-------------------------------------
  59 256 |  0x301    0x303    0x305    0x307
  60 32k |  0x310    0x313    0x316    0x319
  61 64k |  0x311    0x314    0x317    0x31A
  62 16M |  0x312    0x315    0x318    0x31B
  63
  64 To enable one of those modes you have to specify "vga=ask" in the
  65 lilo.conf file and rerun LILO. Then you can type in the desired
  66 mode at the "vga=ask" prompt. For example if you like to use
  67 1024x768x256 colors you have to say "305" at this prompt.
  68
  69 If this does not work, this might be because your BIOS does not support
  70 linear framebuffers or because it does not support this mode at all.
  71 Even if your board does, it might be the BIOS which does not.  VESA BIOS
  72 Extensions v2.0 are required, 1.2 is NOT sufficient.  You will get a
  73 "bad mode number" message if something goes wrong.
  74
  75 1. Note: LILO cannot handle hex, for booting directly with
  76          "vga=mode-number" you have to transform the numbers to decimal.
  77 2. Note: Some newer versions of LILO appear to work with those hex values,
  78          if you set the 0x in front of the numbers.
  79
  80 X11
  81 ===
  82
  83 XF68_FBDev should work just fine, but it is non-accelerated.  Running
  84 another (accelerated) X-Server like XF86_SVGA might or might not work.
  85 It depends on X-Server and graphics board.
  86
  87 The X-Server must restore the video mode correctly, else you end up
  88 with a broken console (and vesafb cannot do anything about this).
  89
  90
  91 Refresh rates
  92 =============
  93
  94 There is no way to change the vesafb video mode and/or timings after
  95 booting linux.  If you are not happy with the 60 Hz refresh rate, you
  96 have these options:
  97
  98  * configure and load the DOS-Tools for the graphics board (if
  99    available) and boot linux with loadlin.
 100  * use a native driver (matroxfb/atyfb) instead if vesafb.  If none
 101    is available, write a new one!
 102  * VBE 3.0 might work too.  I have neither a gfx board with VBE 3.0
 103    support nor the specs, so I have not checked this yet.
 104
 105
 106 Configuration
 107 =============
 108
 109 The VESA BIOS provides protected mode interface for changing
 110 some parameters.  vesafb can use it for palette changes and
 111 to pan the display.  It is turned off by default because it
 112 seems not to work with some BIOS versions, but there are options
 113 to turn it on.
 114
 115 You can pass options to vesafb using "video=vesafb:option" on
 116 the kernel command line.  Multiple options should be separated
 117 by comma, like this: "video=vesafb:ypan,invers"
 118
 119 Accepted options:
 120
 121 invers  no comment...
 122
 123 ypan    enable display panning using the VESA protected mode
 124         interface.  The visible screen is just a window of the
 125         video memory, console scrolling is done by changing the
 126         start of the window.
 127         pro:    * scrolling (fullscreen) is fast, because there is
 128                   no need to copy around data.
 129                 * You'll get scrollback (the Shift-PgUp thing),
 130                   the video memory can be used as scrollback buffer
 131         kontra: * scrolling only parts of the screen causes some
 132                   ugly flicker effects (boot logo flickers for
 133                   example).
 134
 135 ywrap   Same as ypan, but assumes your gfx board can wrap-around
 136         the video memory (i.e. starts reading from top if it
 137         reaches the end of video memory).  Faster than ypan.
 138
 139 redraw  scroll by redrawing the affected part of the screen, this
 140         is the safe (and slow) default.
 141
 142
 143 vgapal  Use the standard vga registers for palette changes.
 144         This is the default.
 145 pmipal  Use the protected mode interface for palette changes.
 146
 147 mtrr:n  setup memory type range registers for the vesafb framebuffer
 148         where n:
 149               0 - disabled (equivalent to nomtrr) (default)
 150               1 - uncachable
 151               2 - write-back
 152               3 - write-combining
 153               4 - write-through
 154
 155         If you see the following in dmesg, choose the type that matches the
 156         old one. In this example, use "mtrr:2".
 157 ...
 158 mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
 159 ...
 160
 161 nomtrr  disable mtrr
 162
 163 vremap:n
 164         remap 'n' MiB of video RAM. If 0 or not specified, remap memory
 165         according to video mode. (2.5.66 patch/idea by Antonino Daplas
 166         reversed to give override possibility (allocate more fb memory
 167         than the kernel would) to 2.4 by tmb@iki.fi)
 168
 169 vtotal:n
 170         if the video BIOS of your card incorrectly determines the total
 171         amount of video RAM, use this option to override the BIOS (in MiB).
 172
 173 Have fun!
 174
 175   Gerd
 176
 177 --
 178 Gerd Knorr <kraxel@goldbach.in-berlin.de>
 179
 180 Minor (mostly typo) changes
 181 by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>